1. Field of the Invention
The invention relates to an image processing circuit and a light illumination module. More particularly, the invention relates to an image processing circuit controlling a backlight of a liquid crystal display (LCD) and a light illumination module providing the backlight of the LCD.
2. Description of Related Art
Light emitting diodes (LEDs) are generally used as light sources, for example, used as a backlight module of a liquid crystal display (LCD), a mobile phone, a portable computer and a personal digital assistant (PDA), etc. The backlight module is a key component used for driving a light source in a display, which not only determines reliability and stability of the display, but also influences display quality of the display.
Generally, to facilitate a user adjusting brightness of the light source or save more power under ambient light, a good dimming ability has to be achieved. In view of physical properties of the LED, a current flowing through the LED and a forward bias of the LED have an exponential relationship, while a lighting degree of the LED is proportional to the current flowing there through. In other words, the greater the current flowing through the LED is, the higher the brightness of the LED is. Commonly used dimming methods include an analog dimming method and a digital dimming method. The analog dimming method is to adjust a magnitude of a forward current flowing through the LED to achieve brightness variation. In the digital dimming method, the LED is controlled to be turned on/off, and based on a visual persistence principle of human eyes, an average brightness is controlled by adjusting a duty cycle for turning on/off the LED. Although the analog dimming method is easy to be implemented, an external circuit has to be added, which increase a system cost. Therefore, the digital dimming method is a current development trend.
Referring to FIG. 1, FIG. 1 is a schematic diagram of a conventional light illumination module 100. The light illumination module 100 can be used to provide a backlight for an LCD, which has a scaler 112 and a driving circuit 122. The scaler 112 and the driving circuit 122 are respectively formed in different integrated circuit (IC) chips, and are respectively disposed on a scaler circuit board 110 and a driving circuit board 120. The scaler 112 receives an image signal SIMG, and converts a resolution of the image signal SIMG from a first resolution to a second resolution, so as to generate and output a control signal DIM[1:4] to the driving circuit 122. The control signal DIM[1:4] is a digital signal of four bits, and each of the four bits is used for controlling a corresponding LED string 160. Each of the LED strings 160 has a plurality of LEDs 162.
Referring to FIG. 1 and FIG. 2, FIG. 2 is a timing diagram of each bit of the control signal DIM[1:4] and a driving voltage VOUT. Each of the bits DIM[1]-DIM[4] is used to turn on/off the corresponding LED string 160. Further, when a value of any of the bits DIM[1]-DIM[4] is “1” (a high level), the corresponding LED string 160 is turned on, and when the value of any of the bits DIM[1]-DIM[4] is “0” (a low level), the corresponding LED string 160 is turned off.
However, since the driving circuit 122 controls the driving voltage VOUT according to sampled voltages of the second ends B of the LED strings 160, and since the voltages of the second ends B are different due to different turning on/off states of the LED strings 160, the voltages of the second ends B sampled by the driving circuit 122 each time are different, so that a voltage value of the driving voltage VOUT is constantly varied. However, the constant variation of the voltage value of the driving voltage VOUT leads to a result that the driving voltage VOUT itself becomes a noise source. In this case, the noise of the light illumination module 100 is increased, and intensity of light provided by the light illumination module 100 is unstable.